1. Field of the Invention
My invention relates to a method for firing direct-fired burners used in industrial furnaces such as soaking pits and reheat furnaces and, more particularly, to side-fired or end-fired furnaces.
2. Description of the Prior Art
Metallurgical and other heat-treating furnaces require precise control of temperature distributions within the furnaces to maintain product quality and consistency. Normally, burners are located at opposite ends of the furnace, and in the case of soaking pits for heating steel ingots, these burners are initially operated at maximum capacity to bring the ingots up to rolling temperature as fast as possible. The firing rate of the burners is thereafter reduced to maintain the proper temperature while the ingots are being thermally soaked. With burners on each end of the furnace, a relatively uniform distribution of heat throughout the furnace is assured.
However, in certain cases it may not be possible to position burners on both ends of the furnace due to design constraints such as reduced clearance on one end of the furnace. This furnace situation is common to retrofit jobs. The alternative is to mount all of the burners on one side of the furnace, but this presents several problems, which were recognized in U.S. Pat. No. 4,475,885 of which I am an inventor. That patent discloses an adjustable flame burner which permits adjustment of the flame characteristics under various operating conditions. Specifically, the burner may yield a short, high release combustion pattern having a large flame diameter with effectively zero forward velocity. Alternatively, the burner may be adjusted to produce an intense flame approximately three times as long as the previously described flame and having an essentially zero radial component. The burner is adjustable between these two extremes to provide a wide variety of flame characteristics. This burner has proven quite successful in soaking pits and side-fired furnace applications.
To date, it has not been possible to utilize fixed flame burners for totally effective heating of side-fired furnaces. Fixed flame burners simply cannot control temperature distribution due to the presence of furnace conditions such as gas movement throughout the furnace, differing stock sizes and differing production rates. Certain attempts have been made to utilize fixed flame burners in side-fired furnaces wherein rich gaseous fuels are supplied to the burner, and the burner is fired at normal rates. However, the quantity of rich gaseous fuel needed to meet a certain heat demand adds little weight to the air/fuel mix and thus the momentum (mass times velocity) of the flame cannot be varied significantly by altering the air/fuel mix. Momentum generally determines how far a flame will travel, and the low momentum flame will not provide sufficient heat to the end of the furnace opposite the burners. It is undesirable to raise fuel velocity as this tends to promote flame separation.
Other attempts have been made in the art to vary the heat release and flame length of a burner by altering the velocity and mixing arrangements of rich gaseous fuels supplied thereto. These methods are known to achieve a minor variation in flame characteristics. The method of firing described herein provides a much greater variation in flame characteristics. Thus, it is an object of the present invention to provide a method for controlling fixed flame and moderately adjustable flame burners in side-fired furnaces and soaking pits utilizing rich gaseous and liquid fuels. It is a further object to assure uniform temperature distribution throughout side-fired furnaces, thereby maintaining product quality. It is a still further object of the invention to introduce heat to the furnace at a rate which is consistent with the desired properties of the stock being heated.